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Friday, January 18, 2013

Q. How much power does my stage system need?

Sound Advice : Mixing

I’m trying to work
out how much power a PA system I work with draws, and I also need to
come up with a sensible ‘plug‑it‑all‑in’ type of procedure. (I’ve read
the Sound On Sound December ‘05 article ‘PA Basics’.) It’s mainly small
venues we play in, such as function rooms and town halls. Looking at the
manual for my Mackie SA1530z, I’m kind of baffled. It says:

Line Input Power Europe: 230V, 50Hz

Recommended Amperage Service: 16 amps

Is
this saying that a 16‑amp circuit is recommended? The spec sheet
doesn’t seem to list how much current the box will draw. Also, it’s
often stated that FOH, mixer and racks, lights and backline should be
powered from their own separate sockets (three in total). Is it
acceptable to power from both sides of a double socket and another
adjacent socket, therefore, all being powered from the same ring main?

Via SOS web site

SOS
Technical Editor Hugh Robjohns replies:

The 16‑amp thing looks like
a generic suggestion to me. In the UK, standard domestic outlets are
nominally 13A anyway!

Essentially, what they are
saying is that it needs to be plugged into a sensible supply. The
typical average current will be a few amps at most, but the initial
inrush current on switch‑on will be considerably higher, so don’t try to
turn everything on in one go!

If you need to
know the real current and power‑consumption figures, invest in something
like an energy monitor, such as the one I’ve found here: www.maplin.co.uk/plug-in-mains-power-and-energy-monitor-38343.
This one is marketed by Maplin in the UK, but I’m sure you’ll find
similar devices from all the usual suppliers. You simply plug in the
device you want to know about, and the display will give you the current
and power being consumed, as well as the supply voltage and frequency.
It’s a really handy device and I use mine a lot when testing and
checking equipment.

Regarding the use of wall
sockets, assuming that you’re working with a PA and backline system that
is consuming less than about 4kW in total (which would be most systems
for a modest‑sized venue), use a double socket to run all the audio
equipment. That minimises any problems with ground loops

If
you need to know how much current your setup is using, a simple energy
monitor like this should do the trick: plug in whatever you’d like to
measure and its power consumption will be displayed.

Run all the backline from one side of the
double outlet, and all the PA (FOH, racks, PA and monitors, for example)
from the other side. Supplying the two systems from their own RCDs
(Residual Current Devices) is essential too, particularly from the point
of view of preventing a backline fault from taking out the PA. If the
musicians want to use their own RCDs for their gear, that’s fine too!

Running
the FOH on a long mains extension from the PA power‑supply socket (or
distribution board) continues the theme of ‘star grounding’ and will
minimise the potential for ground loops in the PA system. Run lighting
from a different socket (or sockets) and try to keep the dimmer racks
and cabling well away from the audio cables.